Conveyor units are typically employed in folding apparatus, for example, for conveying signatures which had been previously cut from a web of an imprinted material.
The signatures each consist of a variable number of sheets which are not connected to each other. For conveying the signatures, it is therefore of great importance that the two endless belts and the cylinder of the conveyor unit move at exactly matched speeds in order to avoid any shearing forces acting on signatures clamped between them, which shearing forces could lead to deformation and to fanning of the signatures in the course of their being transported.
In conventional conveyor units of the above-mentioned type, the first endless belt, which partially loops around the surface of the cylinder, is driven by the cylinder, by friction. Therefore, if no objects are conveyed between them, the path speed of the first belt corresponds to the circumferential speed of the cylinder. If conveyed objects are located in the area of the loop between the cylinder and the first belt, this has an effect on the speed of the first belt, which acts as it would with an increase of the diameter of the cylinder. Therefore, the speed of the first belt increases in accordance with the thickness of the objects to be conveyed. The movement of the second belt is coupled to the rotation of the cylinder at a fixedly set transmission ratio via a speed-transforming gear. Therefore, the speed of the second belt is constant. This results in the two belts only running exactly at the same speed at a defined thickness of the objects to be conveyed, so that the objects are not subjected to shearing forces only during this operating condition.
DE 94 17 127 U1 and EP 0205143 A2 both describe a collection cylinder, against whose circumference a belt system rests and which is provided with sheets via two further cooperating belt systems.
U.S. Pat. No. 5,405,126 describes a folding apparatus with belts driven by an electric motor.
U.S. Pat. No. 3,363,520 discloses a collection cylinder for sheets, having several belts. One belt is driven by the collection cylinder.